SERIAL I/O
7905 Group User’s Manual Rev.1.0
11-21
11.3 Clock synchronous serial I/O mode
fi
2 (n+1)
11.3 Clock synchronous serial I/O mode
Table 11.3.1 lists the performance overview in the clock synchronous serial I/O mode, and Table 11.3.2 lists
the functions of I/O pins in this mode.
Table 11.3.1 Performance overview in clock synchronous serial I/O mode
Item
Transfer data format
Transfer rate
Transmit/Receive control
When selecting internal clock
When selecting external clock
Functions
Transfer data has a length of 8 bits.
LSB first or MSB first can be selected by software.
BRGi’s output divided by 2
Maximum 5 Mbps
CTS function or RTS function can be selected by software.
Table 11.3.2 Functions of I/O pins in clock synchronous serial I/O mode
Functions
Serial data output pin
Programmable I/O port pin
Serial data input pin
Programmable I/O port pin
Transfer clock output pin
Transfer clock input pin
CTS input pin
RTS output pin
Programmable I/O port
Pin name
TxDi (P13, P17, P83)
RxDi (P12, P16, P82)
CLKi (P11, P15, P81)
CTSi, RTSi
(P10, P11, P14, P15,
P80, P81)
Method of selection
TxD0/P13, TxD1/P17, or TxD2/P83 switch bit = “0”
(Dummy data is output when performing only reception.) (Note)
TxD0/P13, TxD1/P17, or TxD2/P83 switch bit = “1”
Port P1 or P8 direction register’s corresponding bit = “0”
– (Can be used as an I/O port pin when performing only transmission.)
Internal/External clock select bit = “0”
Internal/External clock select bit = “1”
See Table 11.2.1.
Port P1 direction register: address 0516
Port P8 direction register: address 1416
Internal/External clock select bit: bit 3 at addresses 3016, 3816, B016
TxD0/P13 switch bit: bit 2 at address AC16
TxD1/P17 switch bit: bit 3 at address AC16
TxD2/P83 switch bit: bit 5 at address AC16
Note: The TxDi pin outputs “H” level until transmission starts after UARTi’s operating mode is selected.
11.3.1 Transfer clock (Synchronizing clock)
Data transfer is performed synchronously with a transfer clock. For the transfer clock, the following selection
is possible:
q Whether to generate a transfer clock internally or to input it from the external.
q Polarity of transfer clock.
The transfer clock is generated by operation of the transmit control circuit. Accordingly, even when performing
only reception, set the transmit enable bit to “1,” and set dummy data in the UARTi transmit buffer register
in order to make the transmit control circuit active.
(1)
Internal generation of transfer clock
The count source selected with the BRG count source select bits is divided by the BRGi, and the
BRGi output is further divided by 2. This divided output is the transfer clock. The transfer clock is
output from the CLKi pin.
Transfer clock’s frequency =
fi: Frequency of BRGi’s count source (f2, f16, f64, or f512)
n: Setting value of BRGi